LHC Challenges and Upgrade Options O. Brüning CERN, Geneva, Switzerland
Contents Introduction Magnet technology Luminosity LHC layout overview Main challenges for the LHC operation LHC parameters Commissioning plan Upgrade options John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 2
Introduction: LHC Goals & Performance Collision energy: Higgs discovery requires E CM > 1 TeV p collisions E beam > 5 TeV LHC: E = 7 TeV = L ⋅ σ event Instantaneous luminosity: # events in detector rare events L > 10 33 cm -2 sec -1 L = 10 34 cm -2 sec -1 ∫ = L ( t ) dt Integrated luminosity: L depends on the beam lifetime, the LHC cycle and ‘turn around’ time and overall accelerator efficiency John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 3
Introduction: the LHC is a Synchrotron ⋅ B circ uniform B field: R = constant = ⋅ ≈ / p q E c π 2 for E >> E 0 realistic synchrotron: B-field is not uniform -drift space for installation -different types of magnets ⋅ q c ∫ = ⋅ ⋅ E B ds -space for experiments etc π 2 high beam energies require: -high magnetic bending field -large circumference -large packing factor John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 4
Introduction: the LHC is a Synchrotron physics goal: E = 7 TeV existing infrastructure: LEP tunnel: circ = 27 km with 22 km arcs assume 80% of arcs can be filled with dipole magnets: F = 0.8 required dipole field for the LHC: 2 π / E c ⋅ = B B = 8.38 T ⋅ q circ F (earth: 0.3 10 -4 T) John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 5
Magnet Technology high beam energies require large rings and high fields 1) Iron joke magnet design 2) air coil magnetdesign -field quality given by pole face geometry -field quality given by coil geometry -field amplified by Ferromagnetic material -SC technology avoids Ohmic losses -iron saturates at 2 T -risk of magnet quenches -Ohmic losses for high magnet currents -field quality changes with time John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 6
Magnet Technology Critical surface of NbTi: -high ambient magnetic field lowers the capability to sustain large current densities -low temperatures increase the capability to sustain large current densities -LHC: B = 8.4 T; T = 1.9 K j = 1 - 2 kA / mm 2 existing machines: Tev: B=4.5T;HERA: B=5.5T; RHIC: B=3.5T He is superfluid below 2K and has a large thermal conductivity! John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 7
Magnet Technology collider ring design requires 2 beams: design with one aperture requires particles & anti-particles Not efficient for a hadron collider! (Tevatron, Chicago USA) 2-ring design implies twice the hardware LHC features novel 2-in-1 magnet design John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 8
Magnet Technology 2-in-1 dipole magnet design with common infrastructure: -15 m long few interconnects (high filling factor) but difficult transport (ca. 30 tons) -compact 2-in-1 design allows p-p collisions in LEP tunnel -corrector magnets at ends tight mechanical tolerances John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 9
Magnet Technology 15 m long, 30 Ton difficult transport & tight tolerances John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 10
Luminosity colliding bunches: ⋅ ⋅ ⋅ n N N f = 1 2 b rev L A = 4 π ⋅ σ ⋅ σ σ = β ⋅ ε A with: x y β is determined by the magnet arrangement & powering ε = ε γ ε n is determined by the injector chain / n goal: high bunch intensity and many bunches L = 10 34 cm -2 sec -1 small β at IP and high collision energy John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 11
LHC Layout 2-in-1 magnet design p-p & Pb-Pb collisions 7 TeV p-beam energy � > 1 TeV CM energy � Higgs discovery 2 high L experiments with L = 10 34 cm -2 sec -1 � 2808 bunches / beam with 1.15 10 11 ppb 2 low L experiments: ALICE (Pb-Pb) & LHCb John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 12
LHC Layout built in old LEP tunnel � 8.4 T dipole magnets CMS � 10 GJ EM energy � powering in 8 sectors 2808 bunches per beam with 1.15 10 11 ppb � 360 MJ / beam � crossing angle & long range beam-beam ATLAS Combined experiment/ LHCB ALICE injection regions Oliver Brüning 13 John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 13
Main Challenges for the Operation Magnetic field perturbations & resonances Collimation efficiency Beam power and machine protection Collective effects and impedance Beam-beam interaction Triplet aperture and beam-beam Electron cloud effect John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 14
LHC Challenges: Field Quality & Resonances tune: Q = number of oscillations per revolution resonances: n Q x + m Q y + r Q s = p; “order” = n+m+r Q y Q y Q x Q x limited accessible area; limit for field quality and Δ Q tolerance John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 15
LHC Challenges: Magnet Field Errors the LHC features 112 circuits / beam (+ orbit correctors) all magnet circuits are tested before and during installation field errors in SC magnets vary with time & operation history � adjustments during operation � non-destructive beam instrumentation John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 16
LHC Challenges: Collimation Efficiency Magnet Quench: � beam abort � several hours of recovery LHC nominal beam intensity: I = 0.5A => 3 10 14 p /beam Quench level: N lost < 7 10 8 m -1 � 2.2 10 -6 N beam ! (compared to 20% to 30% in other superconducting rings) � requires collimation during all operation stages! � requires good optic and orbit control! � feedback loops John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 17
LHC Challenges: Beam Power Magnet quench: � stray particles must not reach the superconducting elements! beam core: 0 to 2 σ primary beam halo: 2 to 6 s; generated by: non-linearities; noise; IBS etc (can damage equipment) secondary halo: 6 to 8 σ; generated by collimators (quench) tertiary halo: > 8 σ; generated by collimators (save) John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 18
LHC Challenges: Beam Power Unprecedented beam power: � potential equipment damage in case of failures during operation � in case of failure the beam must never reach sensitive equipment! John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 19
Beam Power and Machine Protection Unprecedented beam power: � all absorbers and the collimation system must be designed to survive an asynchronous beam dump! (total of up to 136 collimators & absorbers) � Machine protection System! Robust collimator jaw design � fiber reinforced graphite jaws are more robust than Cu jaws � fiber reinforced graphite has a higher impedance and electrical resistivity John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 20
LHC Challenges: Collective Effects resistive wall impedance: � image charges trail behind due to resistivity of surrounding materials � Wake fields drive beam instabilities � effect increases with decreasing gap opening of the collimator jaws � impedance of Graphite jaws either limits the minimum collimator opening � limit for β * or the maximum beam current phased collimation system for the LHC: � Phase 1: graphite jaws for robustness during commissioning � Phase 2: nominal performance (low impedance, non-linear or feedback) John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 21
LHC Challenges: Beam-Beam Interaction beam-beam force: ∝ 1 F additional focusing F ∝ r r for small amplitudes perturbation is proportional to bunch intensity! strong non-linear field: tune & perturbation depends on oscillation amplitude bunch intensity limited by non-linear resonances John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 22
LHC Challenges: Beam-Beam Interaction LHC working point: n+m < 12 Q y Q x = 64.31; Q y = 59.32 total tune spread must be smaller than 0.015! Q x the LHC features 3 proton experiments with bunch intensity limited by beam-beam force: nominal: N < 1.15 10 11 N < 1.5 10 11 ultimate: N < 1.7 10 11 John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 23
LHC Challenges: Triplet Aperture long range beam-beam: Operation with 2808 bunches features approximately 30 unwanted collision points per Interaction Region (IR). � Operation requires crossing angle � aperture reduction! non-linear fields and additional focusing due to beam-beam efficient operation requires large beam separation at unwanted collision points � separation of 9 σ is at the limit of the triplet aperture for nominal β * values! � margins can be introduced by operating with fewer bunches, lower bunch intensities, larger β * values (or larger triplet apertures � upgrade studies) John Adams Seminar; 22. February 2007 Oliver Brüning/CERN AB-ABP 24
Recommend
More recommend
